Conventional mechanical or electromechanical keyswitches provide a tactile response to the user simply as a result of the actuation of the keyswitch. Most modern, and especially portable, keyswitch applications, however, employ shallow keys or keyboards which have limited or no perceivable travel, and no mechanical impact which provides a tactile indication that the key has been actuated.
The typical piezoelectric switch is used in a shallow key arrangement and is actuated by compressing it, also without perceivable travel of the key. Thus, without perceivable travel, there is no tactile response to indicate to the operator that the key has been actuated.
One example of a piezoelectric key in a keyboard is U.S. Pat. No. 5,212,473, Louis, assigned to TypeRight Keyboard Corp., which recognizes the problem of lack of tactile response to a piezoelectric actuator for a key (misnamed "photo-electric" in the drawing) which is directly compressed. The piezoelectric element is mounted on the baseplate of the keyboard so that it will be compressed by pressing on the key. The patent shows conventional pulse generator circuitry which provides a feedback signal to the piezoelectric actuator to cause it to expand slightly. The problem is that such expansion, even at high voltages, is often not perceivable to the operator.
The '473 patent circuitry provides the feedback instantly with the result that the operator is not certain whether any feeling is the result of the operator pressing the key or whether it is the result of feedback.
What is needed is a keyswitch which provides tactile feedback of such strength and timing that it is noticeable by the operator.